1. Field of the Invention
This invention applies to assembling parts in the manufacture of flat tension mask color cathode ray tubes. The invention provides method and means for mapping the path of and positioning an attachment device for affixing a thin tensed foil shadow mask to the mask receiving surface of a mask support structure.
In particular the invention relates to a portion of the process steps employed in the manufacture of the front assembly of a flat tension mask color cathode ray tube. A front assembly includes a glass front panel, planar on one side defined as the inner surface of the glass front panel, a support structure affixed to the inner surface of the panel and a tensed foil shadow mask permanently attached to the support structure with proper registration relative to the color emitting phosphors, applied to the inner surface within the boundaries imposed by the support structure perimeter. Such a front assembly is described in U.S. Pat. No. 4,686,416.
2. Definitions
Certain definitions of terms and phrases used in this disclosure add to the clarity of the description of the invention.
Tube: The term "tube" in this disclosure means a flat tension mask cathode ray tube such as that used as a color television receiver screen or as a color computer monitor screen.
Panel: The front portion of the tube which functions as the viewing screen is a flat glass plate called the "panel".
Mask: An essential part of a tube is a thin metal shadow mask placed close to and behind the inner surface of the panel. In the preferred embodiment of this disclosure, the shadow mask is described as being made of steel and as being permanently affixed to a support structure by means of laser welding.
Support Structure and Rail: For proper functioning of a cathode ray tube, the mask is permanently installed, with proper registration, in a plane fixed at a specified distance from the inner surface of the panel. This specified distance is commonly called the "Q" spacing of the tube and is related to electrical and mechanical geometry of the tube. For the purpose of illustration, the Q spacing of a typical 14" diagonal screen flat tension mask cathode ray tube is approximately 0.290". This dimension is used as the specified distance in the description of the preferred embodiment. The support structure may be part of the panel or made of separate elements attached to the panel. In this document, the metal rectangular structure is called the "support structure". Any one side of the support structure is called a "rail".
Land and Mask Receiving Surface: In preparation for welding, the top surface of the support structure is ground flat. The ground surface of the support structure to which the mask is welded is called the "mask receiving surface" or the "land".
Inner and Outer Surfaces: The surface to which the grill pattern, the phosphor materials, the support structure and the mask are attached and the surface which is ultimately sealed inside the tube is called the "inner surface". The "outer surface" is exposed to view and to the touch after final assembly of the tube.
Mapping: The total process of detecting the position of the edges of the mask receiving surface on the support structure, recording its coordinates and computing the path to be followed by the laser welding head is called "mapping".
3. Reference to Prior Art: There is no known prior art related to mapping the coordinates of a path to be followed by an attachment device for the purpose of affixing a tensed foil shadow mask, called a mask, to the support structure of a flat tension mask cathode ray tube.
4. Problems in the Manufacture of Fixed Mask Tubes: A reason for rigid and permanent attachment of the mask to the support structure of a tube is to maintain mechanical tension on the mask so it retains its shape and exact registration with the color emitting phosphors deposited on the inner surface of the panel during normal operation of the tube.
What follows is a number of the problems addressed and solved by the invention: